Linear demixing or beam forming is the most common method for processing a stream of multiple audio signals with the goal of enhancing a desired acoustic source signal. Multichannel processing methods often rely on the assumptions of linearity and time invariance which are only partially able to describe the acoustic observation. As a result linear filtering is suboptimal for real-world applications and requires the signal to be compensated by non-linear time-varying statistical based post-filtering. Post-filtering approaches generally involve estimation of spectral/temporal masks (or gains) derived by the outputs of the linear filters. While masks generally improve the noise reduction ability, the masking effect could lead to severe degradation of signal quality if the demixing model uncertainty is not taken into account.